For quantified evaluation of the primary stability of cementless femoral stem prostheses the operative faults: too low sized stem, distally short-lined anchoring with proximally surpassing stem and fissure or fracture of the femur shaft were simulated in autoptical test series. By inductive displacement transducers the micromotion between stem and proximal bone layer were measured in medio-lateral and ventro-dorsal direction under static load conditions before and after a dynamic loading of 50,000 cycles. The underdimensioned stem showed its instable anchoring by obviously increased micromotions in all measure plains. The proximally excelling only distally anchored prosthesis demonstrated immense amounts of motion. The fissure doesn't seem to decrease the primary stability of the stems too much. These results of the autoptical test series can only be directly transferred to the conditions of the first weeks after implantation, because the influence of later bone integration could not be considered.

Biomechanical Phenomena↗

PubMedDate not supplied

[Analysis of the protective effect of shock-absorbing shoes for patients treated with hip and knee endoprostheses].

Biomechanical loading of total knee and hip replacement is one of the essential factors which limit the longterm-function of the implant components. A simple and cheap safety provision to avoid mechanical overload seems to be wearing of shock-absorbing shoes. The performed study analyzes the effect of that type of shoe. For judgement the parameters: energy absorption while slow shock, damping while hard shock and safety against sliding were taken. The experiments showed the shock-absorbing shoe is an easy, inexpensive, but very efficient protection measure to improve the longterm-stability of endoprosthesis of the lower extremity.

Biomechanical Phenomena↗

PubMedDate not supplied

[The role of friction in the loosening process of total endoprosthesis of the hip].

Discussing the causes of aseptic loosening mechanism of total hip replacement shear forces resulting from friction between cup and head are often mentioned. Therefore measurements of friction torque in explanted endoprostheses were performed in a new hip simulator to evaluate the influence of friction on the loosening. Differing from other simulators the physiological deformation of the hip bones was imitated by a bending beam. The measured values were compared with mathematically and experimentally found limit loads of the cup fixation. It was shown that the only influence of the shear forces transferred by friction was no significantly dangerous factor for the interface between bone and bone cement of a primarily fixed cup.

Adult↗